Dynamic local oscillator (LO) scheme and switchable receive (RX) chain for carrier aggregation

ABSTRACT

Certain aspects of the present disclosure provide methods and apparatus for dynamically adjusting a voltage-controlled oscillator (VCO) frequency, a local oscillator (LO) divider ratio, and/or a receive path when adding or discontinuing reception of a component carrier (CC) in a carrier aggregation (CA) scheme. This dynamic adjustment is utilized to avoid (or at least reduce) VCO, LO, and transmit signal coupling issues with multiple component carriers, with minimal (or at least reduced) current consumption by the VCO and the LO divider.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/993,334, entitled “DYNAMIC LOCAL OSCILLATOR (LO)SCHEME AND SWITCHABLE RECEIVE (RX) CHAIN FOR CARRIER AGGREGATION” andfiled May 15, 2014, which is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

Certain aspects of the present disclosure generally relate to radiofrequency (RF) circuits for wireless communications and, moreparticularly, to a dynamic local oscillator (LO) scheme andreconfigurable receive paths for carrier aggregation (CA).

BACKGROUND

Wireless communication networks are widely deployed to provide variouscommunication services such as telephony, video, data, messaging,broadcasts, and so on. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. For example, one network may be a 3G (thethird generation of mobile phone standards and technology) system, whichmay provide network service via any one of various 3G radio accesstechnologies (RATs) including EVDO (Evolution-Data Optimized), 1×RTT (1times Radio Transmission Technology, or simply 1×), W-CDMA (WidebandCode Division Multiple Access), UMTS-TDD (Universal MobileTelecommunications System-Time Division Duplexing), HSPA (High SpeedPacket Access), GPRS (General Packet Radio Service), or EDGE (EnhancedData rates for Global Evolution). The 3G network is a wide area cellulartelephone network that evolved to incorporate high-speed internet accessand video telephony, in addition to voice calls. Furthermore, a 3Gnetwork may be more established and provide larger coverage areas thanother network systems. Such multiple access networks may also includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier FDMA (SC-FDMA) networks, 3^(rd) Generation PartnershipProject (3GPP) Long Term Evolution (LTE) networks, and Long TermEvolution Advanced (LTE-A) networks.

A wireless communication network may include a number of base stationsthat can support communication for a number of mobile stations. A mobilestation (MS) may communicate with a base station (BS) via a downlink andan uplink. The downlink (or forward link) refers to the communicationlink from the base station to the mobile station, and the uplink (orreverse link) refers to the communication link from the mobile stationto the base station. A base station may transmit data and controlinformation on the downlink to a mobile station and/or may receive dataand control information on the uplink from the mobile station.

SUMMARY

Certain aspects of the present disclosure generally relate to a dynamiclocal oscillator (LO) scheme and reconfigurable receive paths forcarrier aggregation (CA). This provides for minimal current consumptionwhile maintaining receiver (Rx) de-sense performance (i.e., avoidingvoltage-controlled oscillator (VCO), LO, and transmitter signalcoupling).

Certain aspects of the present disclosure provide a method for wirelesscommunications. The method generally includes receiving and processing afirst component carrier (CC) in a carrier aggregation scheme via a firstreceive path comprising a first low noise amplifier (LNA) and a firstmixer, wherein the first LNA is configured to amplify the first CC andwherein the first mixer is configured to multiply the amplified first CCwith a first LO signal received via a first LO path and generated by afirst frequency synthesizer whose output frequency is divided down by afirst divide ratio to create the first LO signal; adding ordiscontinuing reception of a second CC in the carrier aggregationscheme, the second CC having a different frequency than the first CC;and based on the added or discontinued reception of the second CC, atleast one of: (1) retuning the first frequency synthesizer to adifferent output frequency; (2) changing the first divide ratio; or (3)switching the amplified first CC from being multiplied by the firstmixer to being multiplied by a second mixer with the first LO signalreceived via a second LO path and generated by a second frequencysynthesizer whose output frequency is divided down by a second divideratio to create the first LO signal.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a firstfrequency synthesizer whose output frequency is divided down by a firstdivide ratio to create a first LO signal; a first receive pathconfigured to receive and process a first component carrier (CC) in acarrier aggregation scheme, the first receive path comprising: a firstlow noise amplifier (LNA) configured to amplify the first CC; and afirst mixer configured to multiply the amplified first CC with the firstLO signal received via a first LO path; and a processing system. Theprocessing system is typically configured to add or discontinuereception of a second CC in the carrier aggregation scheme, the secondCC having a different frequency than the first CC; and based on theadded or discontinued reception of the second CC, to at least one of:retune the first frequency synthesizer to a different output frequency;change the first divide ratio; or switch the amplified first CC frombeing multiplied by the first mixer to being multiplied by a secondmixer with the first LO signal received via a second LO path andgenerated by a second frequency synthesizer whose output frequency isdivided down by a second divide ratio to create the first LO signal.

Certain aspects of the present disclosure provide a non-transitorycomputer-readable medium for wireless communications. The mediumgenerally includes instructions stored thereon, which are executable toreceive and process a first CC in a carrier aggregation scheme via afirst receive path comprising a first LNA and a first mixer, wherein thefirst LNA is configured to amplify the first CC and wherein the firstmixer is configured to multiply the amplified first CC with a first LOsignal received via a first LO path and generated by a first frequencysynthesizer whose output frequency is divided down by a first divideratio to create the first LO signal; to add or discontinue reception ofa second CC in the carrier aggregation scheme, the second CC having adifferent frequency than the first CC; and based on the added ordiscontinued reception of the second CC, to at least one of: retune thefirst frequency synthesizer to a different output frequency; change thefirst divide ratio; or switch the amplified first CC from beingmultiplied by the first mixer to being multiplied by a second mixer withthe first LO signal received via a second LO path and generated by asecond frequency synthesizer whose output frequency is divided down by asecond divide ratio to create the first LO signal.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forsynthesizing a first frequency; means for frequency dividing the firstfrequency by a first divide ratio to create a first LO signal; means forreceiving and processing a first CC in a carrier aggregation scheme,comprising: means for amplifying the first CC and first means for mixingthe amplified first CC with the first LO signal received via a first LOpath; means for adding or discontinuing reception of a second CC in thecarrier aggregation scheme, the second CC having a different frequencythan the first CC; and means for selecting, based on the added ordiscontinued reception of the second CC, between at least one of:retuning the means for synthesizing the first frequency to a differentoutput frequency; changing the first divide ratio; or switching theamplified first CC from being mixed by the first means for mixing tobeing mixed by a second means for mixing with the first LO signalreceived via a second LO path and generated by means for synthesizing asecond frequency that is divided down by a second divide ratio to createthe first LO signal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a diagram of an example wireless communications network inaccordance with certain aspects of the present disclosure.

FIG. 2 is a block diagram of an example access point (AP) and exampleuser terminals in accordance with certain aspects of the presentdisclosure.

FIG. 3 is a block diagram of an example transceiver front end inaccordance with certain aspects of the present disclosure.

FIG. 4 is a table of example frequency band combinations for downlinkcarrier aggregation (CA) in different regions, in accordance withcertain aspects of the present disclosure.

FIG. 5A is a table of example local oscillator (LO) divide ratios fordifferent CA frequency synthesizers, in accordance with certain aspectsof the present disclosure.

FIG. 5B is a reorganized version of the table in FIG. 5A, adding examplevoltage-controlled oscillator (VCO) and LO divider current consumption,in accordance with certain aspects of the present disclosure.

FIG. 6 is a table providing a number of coupling violations for variousexample CA frequency band combinations of B1, B3, B7 and B28, inaccordance with certain aspects of the present disclosure.

FIGS. 7A-7D illustrate a dynamic LO scheme and receive pathconfiguration, when sequentially adding downlink component carriers(CCs), in accordance with certain aspects of the present disclosure.

FIG. 8 is a bar graph comparing example current consumption between adynamic LO scheme and a static LO scheme for different numbers ofdownlink CCs, in accordance with certain aspects of the presentdisclosure.

FIG. 9A provides a bar graph and a corresponding table of VCOfrequencies for different numbers of downlink CCs for a dynamic LOscheme, in accordance with certain aspects of the present disclosure.

FIG. 9B provides a bar graph and a corresponding table of VCOfrequencies for different numbers of downlink CCs for a static LOscheme, in accordance with certain aspects of the present disclosure.

FIG. 10 is a flow diagram of example operations for implementing adynamic LO scheme and switchable receive paths, in accordance withcertain aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the present disclosure are described below. It shouldbe apparent that the teachings herein may be embodied in a wide varietyof forms and that any specific structure, function, or both beingdisclosed herein is merely representative. Based on the teachingsherein, one skilled in the art should appreciate that an aspectdisclosed herein may be implemented independently of any other aspectsand that two or more of these aspects may be combined in various ways.For example, an apparatus may be implemented or a method may bepracticed using any number of the aspects set forth herein. In addition,such an apparatus may be implemented or such a method may be practicedusing other structure, functionality, or structure and functionality inaddition to or other than one or more of the aspects set forth herein.Furthermore, an aspect may comprise at least one element of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

The techniques described herein may be used in combination with variouswireless technologies such as Code Division Multiple Access (CDMA),Orthogonal Frequency Division Multiplexing (OFDM), Time DivisionMultiple Access (TDMA), Spatial Division Multiple Access (SDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), Time DivisionSynchronous Code Division Multiple Access (TD-SCDMA), and so on.Multiple user terminals can concurrently transmit/receive data viadifferent (1) orthogonal code channels for CDMA, (2) time slots forTDMA, or (3) sub-bands for OFDM. A CDMA system may implement IS-2000,IS-95, IS-856, Wideband-CDMA (W-CDMA), or some other standards. An OFDMsystem may implement Institute of Electrical and Electronics Engineers(IEEE) 802.11, IEEE 802.16, Long Term Evolution (LTE) (e.g., in TDDand/or FDD modes), or some other standards. A TDMA system may implementGlobal System for Mobile Communications (GSM) or some other standards.These various standards are known in the art.

An Example Wireless System

FIG. 1 illustrates a wireless communications system 100 with accesspoints 110 and user terminals 120. For simplicity, only one access point110 is shown in FIG. 1. An access point (AP) is generally a fixedstation that communicates with the user terminals and may also bereferred to as a base station (BS), an evolved Node B (eNB), or someother terminology. A user terminal (UT) may be fixed or mobile and mayalso be referred to as a mobile station (MS), an access terminal, userequipment (UE), a station (STA), a client, a wireless device, or someother terminology. A user terminal may be a wireless device, such as acellular phone, a personal digital assistant (PDA), a handheld device, awireless modem, a laptop computer, a tablet, a personal computer, etc.

Access point 110 may communicate with one or more user terminals 120 atany given moment on the downlink and uplink. The downlink (i.e., forwardlink) is the communication link from the access point to the userterminals, and the uplink (i.e., reverse link) is the communication linkfrom the user terminals to the access point. A user terminal may alsocommunicate peer-to-peer with another user terminal. A system controller130 couples to and provides coordination and control for the accesspoints.

System 100 employs multiple transmit and multiple receive antennas fordata transmission on the downlink and uplink. Access point 110 may beequipped with a number N_(ap) of antennas to achieve transmit diversityfor downlink transmissions and/or receive diversity for uplinktransmissions. A set N_(u) of selected user terminals 120 may receivedownlink transmissions and transmit uplink transmissions. Each selecteduser terminal transmits user-specific data to and/or receivesuser-specific data from the access point. In general, each selected userterminal may be equipped with one or multiple antennas (i.e., N_(ut)≧1).The N_(u) selected user terminals can have the same or different numberof antennas.

Wireless system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. System 100 may alsoutilize a single carrier or multiple carriers for transmission. Eachuser terminal may be equipped with a single antenna (e.g., in order tokeep costs down) or multiple antennas (e.g., where the additional costcan be supported).

FIG. 2 shows a block diagram of access point 110 and two user terminals120 m and 120 x in wireless system 100. Access point 110 is equippedwith N_(ap) antennas 224 a through 224 ap. User terminal 120 m isequipped with N_(ut,m) antennas 252 ma through 252 mu, and user terminal120 x is equipped with N_(ut,x) antennas 252 xa through 252 xu. Accesspoint 110 is a transmitting entity for the downlink and a receivingentity for the uplink. Each user terminal 120 is a transmitting entityfor the uplink and a receiving entity for the downlink. As used herein,a “transmitting entity” is an independently operated apparatus or devicecapable of transmitting data via a frequency channel, and a “receivingentity” is an independently operated apparatus or device capable ofreceiving data via a frequency channel. In the following description,the subscript “dn” denotes the downlink, the subscript “up” denotes theuplink, N_(up) user terminals are selected for simultaneous transmissionon the uplink, N_(dn) user terminals are selected for simultaneoustransmission on the downlink, N_(up) may or may not be equal to N_(dn),and N_(up) and N_(dn) may be static values or can change for eachscheduling interval. Beam-steering or some other spatial processingtechnique may be used at the access point and user terminal.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic data{d_(up)} for the user terminal based on the coding and modulationschemes associated with the rate selected for the user terminal andprovides a data symbol stream {s_(up)} for one of the N_(ut,m) antennas.A transceiver front end (TX/RX) 254 (also known as a radio frequencyfront end (RFFE)) receives and processes (e.g., converts to analog,amplifies, filters, and frequency upconverts) a respective symbol streamto generate an uplink signal. The transceiver front end 254 may alsoroute the uplink signal to one of the N_(ut,m) antennas for transmitdiversity via an RF switch, for example. The controller 280 may controlthe routing within the transceiver front end 254. Memory 282 may storedata and program codes for the user terminal 120 and may interface withthe controller 280.

A number N_(up) of user terminals may be scheduled for simultaneoustransmission on the uplink. Each of these user terminals transmits itsset of processed symbol streams on the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. For receive diversity, a transceiver front end 222 may selectsignals received from one of the antennas 224 for processing. Forcertain aspects of the present disclosure, a combination of the signalsreceived from multiple antennas 224 may be combined for enhanced receivediversity. The access point's transceiver front end 222 also performsprocessing complementary to that performed by the user terminal'stransceiver front end 254 and provides a recovered uplink data symbolstream. The recovered uplink data symbol stream is an estimate of a datasymbol stream {s_(up)} transmitted by a user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)the recovered uplink data symbol stream in accordance with the rate usedfor that stream to obtain decoded data. The decoded data for each userterminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230 andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal TX dataprocessor 210 may provide a downlink data symbol streams for one of moreof the N_(dn) user terminals to be transmitted from one of the N_(ap)antennas. The transceiver front end 222 receives and processes (e.g.,converts to analog, amplifies, filters, and frequency upconverts) thesymbol stream to generate a downlink signal. The transceiver front end222 may also route the downlink signal to one or more of the N_(ap)antennas 224 for transmit diversity via an RF switch, for example. Thecontroller 230 may control the routing within the transceiver front end222. Memory 232 may store data and program codes for the access point110 and may interface with the controller 230.

At each user terminal 120, N_(ut,m) antennas 252 receive the downlinksignals from access point 110. For receive diversity at the userterminal 120, the transceiver front end 254 may select signals receivedfrom one of the antennas 252 for processing. For certain aspects of thepresent disclosure, a combination of the signals received from multipleantennas 252 may be combined for enhanced receive diversity. The userterminal's transceiver front end 254 also performs processingcomplementary to that performed by the access point's transceiver frontend 222 and provides a recovered downlink data symbol stream. An RX dataprocessor 270 processes (e.g., demodulates, deinterleaves, and decodes)the recovered downlink data symbol stream to obtain decoded data for theuser terminal.

Those skilled in the art will recognize the techniques described hereinmay be generally applied in systems utilizing any type of multipleaccess schemes, such as TDMA, SDMA, Orthogonal Frequency DivisionMultiple Access (OFDMA), CDMA, SC-FDMA, TD-SCDMA, and combinationsthereof.

FIG. 3 is a block diagram of an example transceiver front end 300, suchas transceiver front ends 222, 254 in FIG. 2, in accordance with certainaspects of the present disclosure. The transceiver front end 300includes a transmit (TX) path 302 (also known as a transmit chain) fortransmitting signals via one or more antennas and a receive (RX) path304 (also known as a receive chain) for receiving signals via theantennas. If the TX path 302 and the RX path 304 share an antenna 303,the paths may be connected with the antenna via an interface 306, whichmay include any of various suitable RF devices, such as a duplexer, aswitch, a diplexer, and the like.

Receiving in-phase (I) or quadrature (Q) baseband analog signals from adigital-to-analog converter (DAC) 308, the TX path 302 may include abaseband filter (BBF) 310, a mixer 312, a driver amplifier (DA) 314, anda power amplifier 316. The BBF 310, the mixer 312, and the DA 314 may beincluded in a radio frequency integrated circuit (RFIC), while the PA316 is often external to the RFIC. The BBF 310 filters the basebandsignals received from the DAC 308, and the mixer 312 mixes the filteredbaseband signals with a transmit local oscillator (LO) signal to convertthe baseband signal of interest to a different frequency (e.g.,upconvert from baseband to RF). This frequency conversion processproduces the sum and difference frequencies of the LO frequency and thefrequency of the signal of interest. The sum and difference frequenciesare referred to as the beat frequencies. The beat frequencies aretypically in the RF range, such that the signals output by the mixer 312are typically RF signals, which are amplified by the DA 314 and by thePA 316 before transmission by the antenna 303.

The RX path 304 includes a low noise amplifier (LNA) 322, a mixer 324,and a baseband filter (BBF) 326. The LNA 322, the mixer 324, and the BBF326 may be included in a radio frequency integrated circuit (RFIC),which may or may not be the same RFIC that includes the TX pathcomponents. RF signals received via the antenna 303 may be amplified bythe LNA 322, and the mixer 324 mixes the amplified RF signals with areceive local oscillator (LO) signal to convert the RF signal ofinterest to a different baseband frequency (i.e., downconvert). Thebaseband signals output by the mixer 324 may be filtered by the BBF 326before being converted by an analog-to-digital converter (ADC) 328 todigital I or Q signals for digital signal processing.

While it is desirable for the output of an LO to remain stable infrequency, tuning to different frequencies indicates using avariable-frequency oscillator, which involves compromises betweenstability and tunability. Contemporary systems employ frequencysynthesizers with a voltage-controlled oscillator (VCO) to generate astable, tunable LO with a particular tuning range. Thus, the transmit LOis typically produced by a TX frequency synthesizer 318, which may bebuffered or amplified by amplifier 320 (and/or frequency divided) beforebeing mixed with the baseband signals in the mixer 312. Similarly, thereceive LO is typically produced by an RX frequency synthesizer 330,which may be buffered or amplified by amplifier 332 (and/or frequencydivided) before being mixed with the RF signals in the mixer 324.

Example Dynamic LO Scheme and Switchable RX Chain in Carrier Aggregation

Carrier aggregation is used in some radio access technologies (RATs),such as LTE-A, in an effort to increase the bandwidth, and therebyincrease bitrates. In carrier aggregation, multiple frequency resources(i.e., carriers) are allocated for sending data. Each aggregated carrieris referred to as a component carrier (CC). In LTE Rel-10, for example,up to five component carriers can be aggregated, leading to a maximumaggregated bandwidth of 100 MHz. The allocation of resources may becontiguous or non-contiguous. Non-contiguous allocation may be eitherintra-band (i.e., the component carriers belong to the same operatingfrequency band, but have one or more gaps in between) or inter-band, inwhich case the component carriers belong to different operatingfrequency bands.

In LTE-A carrier aggregation (CA), multiple carriers are used in amobile transceiver to increase data throughput. Each carrier utilizes avoltage-controlled oscillator (VCO) to generate its local oscillator(LO) frequency. To minimize, or at least reduce, coupling of the VCOsamong themselves and between VCOs and transmitter (TX) signals, acomprehensive VCO frequency plan and LO divide ratio scheme may be used.This allows the same LO frequency to be generated in different ways,such that for certain CA frequency band combinations, one or a fewVCO/LO combinations will yield the minimum coupling and Rx de-sense.Contemporary solutions include: (1) pre-assigning VCO frequency plan andLO divide ratio to the given CA combination; and (2) using digitalcoupling cancellation, such as non-linear interference cancellation(NLIC). Both solutions have a current penalty (i.e., unnecessarilyconsume more current) compared with certain aspects of the presentdisclosure.

Instead of the static LO scheme, certain aspects of the presentdisclosure provide dynamic LO generation. The lowest current consumptionfor one downlink component carrier (1DL) is the starting point if thereis no CA coupling (e.g., use CA frequency synthesizer CA1). Then, ifmore downlink component carrier options are available, the minimumcurrent solution is chosen for 2DL or 3DL, for example. The dynamic LOscheme will converge to the same current consumption as the staticscheme when the maximum number of downlink component carriers isreached. From 1DL to the maximum number of downlink component carriers,the VCO may be retuned for a new configuration, the LO divide ratio maybe changed, and/or the receive path may be switched to a different mixerwith a different LO drive (e.g., a different LNA), all in an effort toachieve minimum coupling while consuming the lowest current.

Each carrier has different CA frequency band combinations in differentregions. The table 400 in FIG. 4 provides some examples for 4 downlinkcomponent carrier (4DL) carrier aggregation. The frequency bandcombination B1/B3/B7/B28 (the third row in the table 400) is used forillustrative purposes in the present disclosure, but the ideas presentedherein apply to any frequency band combination.

To avoid VCO and LO coupling, a comprehensive scheme involving a VCOfrequency plan, a particular LO divide ratio, and a certain receivechain configuration may be utilized. This allows the LO frequency of thesame band to be generated in different ways. For example, over 90different VCO/LO coupling mechanisms may be analyzed for each bandcombination with different frequency and LO divide ratios. If one of thefollowing equations is satisfied, there is a coupling violation:

${{{f\_ VCO}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{Tx} \\{GPS}\end{Bmatrix}} \pm {\begin{Bmatrix}1 \\2\end{Bmatrix}{f\_ Tx}}} = {{f\_ sig}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{GPS}\end{Bmatrix}}$ ${{{{f\_ VCO}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{Tx} \\{GPS}\end{Bmatrix}} \pm {{f\_ VCO}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{Tx} \\{GPS}\end{Bmatrix}}} \pm {f\_ Tx}} = {{f\_ sig}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{GPS}\end{Bmatrix}}$ ${{{f\_ VCO}\begin{Bmatrix}{PRx} \\{SRx} \\{TRx} \\{Tx} \\{GPS}\end{Bmatrix}} \pm {\begin{Bmatrix}1 \\2\end{Bmatrix}{f\_ Tx}}} = 0$where f_VCO is the VCO frequency, f_Tx is the transmitter frequency,f_sig is the receive signal frequency, PRx is the primary receiver (Rx),SRx is the secondary receiver, TRx is the tertiary receiver, Tx is thetransmitter, and GPS is the Global Positioning System.

FIG. 5A is a table 500 of example LO divide ratios for four different CAfrequency synthesizers (CA0-CA3) and the transmitter (TX), in accordancewith certain aspects of the present disclosure. To achieve minimumcoupling for a given 4DL CA combination, certain VCO frequency and LOdivide ratios (e.g., div2, div3, and div6) are implicated. For example,for the combination B1+B3+B7+B28, B1 (CA2 div3)+B3 (CA3 div2)+B28 (CA1div6)+B7 (CA0 div2) may be desired for zero coupling violations. B28 isa low frequency band (LB), B1 and B3 are mid frequency bands (MB), andB7 is a high frequency band (HB) according to the table 400.

Although the same LO frequency may be generated with different CAfrequency synthesizers and divide ratios, the current consumption may bevery different, as illustrated in table 550 of FIG. 5B. The table 550 isa reorganized version of the table 500 of FIG. 5A, with the addition ofexample VCO and LO divider current consumption values.

FIG. 6 is a table 600 providing a number of coupling violations forvarious example CA frequency band combinations of B1, B3, B7, and B28,in accordance with certain aspects of the present disclosure. In thetable 600, “Pcell” is the primary cell band, where the transmitter (Tx)is in the Pcell, “Scell” is the secondary cell band, “Tcell” is thetertiary cell band, “PT” is the primary transmitter, “PR” is the primaryRx, “SR” is the secondary Rx, and “TR” is the tertiary Rx. Also in thetable 600, “div_” is the LO divide ratio (e.g., ranging from 2 to 12),and “VCO_” is the CA frequency synthesizer.

If the assignment of B1 to CA2/div3, B3 to CA3/div2, B28 to CA1/div6,and B7 to CA0/div2 is fixed, this assignment should have the minimumcoupling violation when all four downlink CCs are used as in the secondrow of the table 600. However, for a one downlink (1DL) componentcarrier case (which is non-CA) in B1, B3, or B7, the current consumptionis not optimal compared to the case where the CA1 frequency synthesizeris used for these bands (instead of B28). Similarly for a 2DL case,B1+B3 with CA2/div3+CA3/div2 consumes more current thanCA1/div2+CA3/div2.

Note that the 4DL case may have any sequence of bring-up from 1DL to4DL. As an example, B1→B1+B3→B1+B3+B28→B1+B3+B28+B7. As an alternativeexample, B3→B3+B7→B3+B7+B1→B3+B7+B1+B28.

Instead of the static LO scheme, certain aspects, of the presentdisclosure provide a dynamic LO generation. Certain aspects maytypically start for 1DL with the lowest current solution if there is noCA coupling (e.g., CA1). Then as CCs are added, the minimum currentsolution for 2DL or 3DL may be chosen if more minimum coupling violationoptions are available. By design, this dynamic LO scheme will convergeto the same current consumption as the static LO scheme when the numberof downlink components carriers reaches the maximum number of DL CCs(max DL).

From 1DL to max DL, the VCO in the CA frequency synthesizer may beretuned for the new configuration, the LO divide ratio may be changed,and/or the receive path may be reconfigured, for example, by switchingto a different mixer with a different LO drive (e.g., different LNA). Inthis manner, minimum coupling may be achieved while consuming thelowest, or at least reduced, current.

FIGS. 7A-7D illustrate a dynamic LO scheme and receive pathconfiguration, when sequentially adding downlink component carriers(1DL→2DL→3DL→4DL), in accordance with certain aspects of the presentdisclosure. The sequence may occur in reverse with the sameconfigurations when sequentially discontinuing reception of downlink CCs(4DL→3DL→2DL→1DL).

In the configuration 700 of FIG. 7A, the frequency synthesizer with thelowest current consumption (e.g., CA1 VCO 704) is used for 1DL, wherecoupling from other VCOs is not an issue. Here, a received componentcarrier in B1 is amplified by an LNA 702, and a mixer 706 multiplies theamplified B1 CC with an LO signal 708 provided by CA1 with an LO divideratio of div2. With B1 being an MB, note that the CA1 div2 scheme hasthe lowest total current consumption of 21 mA, with the VCO currentbeing 12 mA and the divider current being 9 mA as illustrated in thetable 550 of FIG. 5B.

In the configuration 730 of FIG. 7B, a component carrier in B28 isadded. Therefore, the CA3 VCO 732 is enabled, and the component carrierin B1 is now moved to CA3 with a divide ratio of div3 by switching to adifferent mixer 734 for B1. The component carrier in B28 is amplified byanother LNA 736, and a mixer 738 multiplies the amplified B28 CC with anLO signal 740 provided by CA1 with a different LO divide ratio of div6.The CA1 VCO is also retuned to B28.

In the configuration 760 of FIG. 7C, a component carrier in B7 is added.Therefore, the CA2 VCO 762 is enabled, and the B1 CC is now moved to CA2with a div4 divide ratio by switching to yet another mixer 764 for B1.The CA3 VCO 732 is retuned to B7, the B7 CC is amplified by yet anotherLNA 766, and a mixer 768 multiplies the amplified B7 CC with an LOsignal 770 provided by CA3 with a different LO divide ratio of div2.

In the configuration 390 of FIG. 7D, a component carrier in B3 is added.Consequently, the CA0 VCO 792 is enabled, and the B7 CC is now moved toCA0 with a div2 divide ratio by switching to a different mixer 794 forB7. The B1 CC remains with CA2 but a different LO divide ratio of div3is used. The CA3 VCO 732 is retuned to B3, the B3 CC is amplified by yetanother LNA 796, and the mixer 734 multiplies the amplified B3 CC withan LO signal 798 provided by CA3 with a div2 divide ratio.

FIG. 8 is a bar graph 800 and a corresponding table 820 comparingexample current consumption between a dynamic LO scheme and a static LOscheme for different numbers of downlink CCs, in accordance with certainaspects of the present disclosure. Note that the dynamic and static LOschemes have similar current consumption when using the maximum numberof downlink component carriers (4DL in this case), but that the dynamicLO scheme has considerably lower current consumption in the cases withfewer downlink component carriers.

FIG. 9A provides a bar graph 900 and a corresponding table 910 of VCOfrequencies for different numbers of downlink CCs for a dynamic LOscheme, in accordance with certain aspects of the present disclosure.For the dynamic LO scheme, more VCO spectra show up as more downlinkcomponent carriers are added. The VCO spectra of existing downlink CCsmay change as carriers are added or removed, as illustrated here for B1.

FIG. 9B provides a bar graph 950 and a corresponding table 960 of VCOfrequencies for different numbers of downlink CCs for a static LOscheme, in accordance with certain aspects of the present disclosure.For the static LO scheme, the VCO spectra of existing downlink componentcarriers do not change as carriers are added or removed, in contrastwith the bar graph 900 of FIG. 9A.

FIG. 10 is a flow diagram of example operations 1000 for implementing adynamic LO scheme and switchable receive paths, in accordance withcertain aspects of the present disclosure. The operations 1000 may beperformed by an apparatus for wireless communications, such as a basestation or a mobile station.

The operations 1000 may begin, at 1002, by receiving and processing afirst CC in a carrier aggregation scheme via a first receive path. Thefirst receive path may include a first LNA and a first mixer. The firstLNA is configured to amplify the first CC, and the first mixer isconfigured to multiply the amplified first CC with a first LO signalreceived by a first LO path and generated by a first frequencysynthesizer whose output frequency is divided down by a first divideratio to create the first LO signal.

At 1004, reception of a second CC in the carrier aggregation scheme maybe added or discontinued. In other words, the number of downlink CCs maybe increased or decreased, respectively. While the second CC has adifferent frequency than the first CC, the second CC may be in the sameor a different Evolved UMTS (Universal Mobile Telecommunications System)Terrestrial Radio Access (E-UTRA) frequency band than the first CC.

Based on the added or discontinued reception of the second CC at 1004,at least one of the following operations may occur at 1006: (1) retuningthe first frequency synthesizer to a different output frequency; (2)changing the first divide ratio; or (3) switching the amplified first CCfrom being multiplied by the first mixer to being multiplied by a secondmixer with the first LO signal received via a second LO path andgenerated by a second frequency synthesizer whose output frequency isdivided down by a second divide ratio to create the first LO signal.

According to certain aspects, the first frequency synthesizer has thelowest current consumption of all frequency synthesizers for the carrieraggregation scheme when the first CC is the only component carrier.

According to certain aspects, the least one of the retuning, thechanging, or the switching is selected based on at least one of: (1)current consumption associated with the first and second divide ratiosand with the first and second frequency synthesizers; or (2) couplingbetween at least one of the first LO signal, the first componentcarrier, the second component carrier, a first or second harmonic of atransmit signal, or an LO signal associated with the transmit signal.

According to certain aspects, adding reception of the second CC involvesreceiving and processing the second CC via a second receive path. Thesecond receive path includes a second LNA and a third mixer. The secondLNA is configured to amplify the second CC, and the third mixer isconfigured to multiply the amplified second CC with a second LO signalreceived via a third LO path and generated by a third frequencysynthesizer whose output frequency is divided down by a third divideratio to create the second LO signal. For certain aspects, the thirdfrequency synthesizer is the same as the first frequency synthesizer.

According to certain aspects, the operations 1000 may further involveadding or discontinuing reception of a third CC in the carrieraggregation scheme. The third CC has a different frequency than thefirst and second CCs. Based on the added or discontinued reception ofthe third CC, at least one of the following operations may occur: (1)retuning at least one of the first, second, or third frequencysynthesizer to a different output frequency; (2) changing at least oneof the first, second, or third divide ratio; (3) switching the amplifiedfirst CC from being multiplied by the first mixer to being multiplied bythe second mixer; (4) switching the amplified first CC from beingmultiplied by the second mixer to being multiplied by the first mixer;or (5) switching the amplified first CC from being multiplied by thefirst or second mixer to being multiplied by a fourth mixer with thefirst LO signal received via a fourth LO path and generated by a fourthfrequency synthesizer whose output frequency is divided down by a fourthdivide ratio to create the first LO signal. For certain aspects, addingreception of the third CC includes receiving and processing the third CCvia a third receive path comprising a third LNA and a fifth mixer,wherein the third LNA is configured to amplify the third CC, and whereinthe fifth mixer is configured to multiply the amplified third CC with athird LO signal received via a fifth LO path and generated by a fifthfrequency synthesizer whose output frequency is divided down by a fifthdivide ratio to create the third LO signal. The fifth frequencysynthesizer may be the same as the first, second, third, or fourthfrequency synthesizer (e.g., in a case where there are only 4 CAfrequency synthesizers).

According to certain aspects, the operations 1000 may further includeadding or discontinuing reception of a fourth CC in the carrieraggregation scheme. The fourth CC has a different frequency than thefirst, second, and third CCs. Based on the added or discontinuedreception of the fourth CC, at least one of the following operations mayoccur: (1) retuning at least one of the first, second, third, or fourthfrequency synthesizer to a different output frequency; (2) changing atleast one of the first, second, third, or fourth divide ratio; (3)switching the amplified first CC from being multiplied by the firstmixer to being multiplied by the second or fourth mixer; (4) switchingthe amplified first CC from being multiplied by the second mixer tobeing multiplied by the first or fourth mixer; (5) switching theamplified first CC from being multiplied by the fourth mixer to beingmultiplied by the first or second mixer; or (6) switching the amplifiedfirst CC from being multiplied by the first, second, or fourth mixer tobeing multiplied by a sixth mixer with the first LO signal received viaa sixth LO path and generated by a sixth frequency synthesizer whoseoutput frequency is divided down by a sixth divide ratio to create thefirst LO signal. For certain aspects, adding reception of the fourth CCinvolves receiving and processing the fourth CC via a fourth receivepath having a fourth LNA and a seventh mixer. The fourth LNA isconfigured to amplify the fourth CC, and the seventh mixer is configuredto multiply the amplified fourth CC with a fourth LO signal received viaa seventh LO path and generated by a seventh frequency synthesizer whoseoutput frequency is divided down by a seventh divide ratio to create thefourth LO signal. The seventh frequency synthesizer may be the same asthe second frequency synthesizer, and the seventh mixer may be the sameas the second mixer. For certain aspects, the sixth frequencysynthesizer is not the first, second, or third frequency synthesizer.

The various operations or methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

For example, means for transmitting may comprise a transmitter (e.g.,the transceiver front end 254 of the user terminal 120 depicted in FIG.2 or the transceiver front end 222 of the access point 110 shown in FIG.2) and/or an antenna (e.g., the antennas 252 ma through 252 mu of theuser terminal 120 m portrayed in FIG. 2 or the antennas 224 a through224 ap of the access point 110 illustrated in FIG. 2). Means forreceiving may comprise a receiver (e.g., the transceiver front end 254of the user terminal 120 depicted in FIG. 2 or the transceiver front end222 of the access point 110 shown in FIG. 2) and/or an antenna (e.g.,the antennas 252 ma through 252 mu of the user terminal 120 m portrayedin FIG. 2 or the antennas 224 a through 224 ap of the access point 110illustrated in FIG. 2). Means for synthesizing a frequency (or anoscillating signal having a particular frequency) may comprise afrequency synthesizer, such as the RX frequency synthesizer 330 of FIG.3, which may include a phase-locked loop (PLL) having a VCO. Means forfrequency dividing may comprise a frequency divider, such as a frequencydivider for generating an LO. Means for receiving and processing maycomprise a receive path (i.e., a receive chain), such as the RX path 304of FIG. 3. Means for amplifying may comprise an amplifier, such as theLNA 322 of FIG. 3 or the LNAs 702, 736, 766, and 796 of FIG. 7D. Meansfor mixing may comprise a mixer, such as the mixer 324 of FIG. 3 or themixers 738, 764, 734, and 794 of FIG. 7D.

Means for processing, means for adding or discontinuing reception, meansfor selecting, or means for determining may comprise a processingsystem, which may include one or more processors, such as the RX dataprocessor 270, the TX data processor 288, and/or the controller 280 ofthe user terminal 120 illustrated in FIG. 2. Additionally oralternatively, means for adding or discontinuing reception or means forselecting may comprise an interface between antennas and a receive path,such as the interface 306 of FIG. 3. For example, a processing system(as described in the previous sentence) may control this interface.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, a-b-c, as well as any combination with multiples of thesame element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b,b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in hardware, anexample hardware configuration may comprise a processing system in awireless node. The processing system may be implemented with a busarchitecture. The bus may include any number of interconnecting busesand bridges depending on the specific application of the processingsystem and the overall design constraints. The bus may link togethervarious circuits including a processor, machine-readable media, and abus interface. The bus interface may be used to connect a networkadapter, among other things, to the processing system via the bus. Thenetwork adapter may be used to implement the signal processing functionsof the PHY layer. In the case of a user terminal 120 (see FIG. 1), auser interface (e.g., keypad, display, mouse, joystick, etc.) may alsobe connected to the bus. The bus may also link various other circuitssuch as timing sources, peripherals, voltage regulators, powermanagement circuits, and the like, which are well known in the art, andtherefore, will not be described any further.

The processor may be responsible for managing the bus and generalprocessing, including the execution of software stored on themachine-readable media. The processor may be implemented with one ormore general-purpose and/or special-purpose processors. Examples includemicroprocessors, microcontrollers, DSP processors, and other circuitrythat can execute software. Software shall be construed broadly to meaninstructions, data, or any combination thereof, whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Machine-readable media may include, by way ofexample, RAM (Random Access Memory), flash memory, ROM (Read OnlyMemory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product. The computer-program product may comprisepackaging materials.

In a hardware implementation, the machine-readable media may be part ofthe processing system separate from the processor. However, as thoseskilled in the art will readily appreciate, the machine-readable media,or any portion thereof, may be external to the processing system. By wayof example, the machine-readable media may include a transmission line,a carrier wave modulated by data, and/or a computer-readable storagemedium with instructions stored thereon separate from the wireless node,all of which may be accessed by the processor through the bus interface.Alternatively, or in addition, the machine-readable media, or anyportion thereof, may be integrated into the processor, such as the casemay be with cache and/or general register files.

The processing system may be configured as a general-purpose processingsystem with one or more microprocessors providing the processorfunctionality and external memory providing at least a portion of themachine-readable media, all linked together with other supportingcircuitry through an external bus architecture. Alternatively, theprocessing system may be implemented with an ASIC (Application SpecificIntegrated Circuit) with the processor, the bus interface, the userinterface in the case of an access terminal), supporting circuitry, andat least a portion of the machine-readable media integrated into asingle chip, or with one or more FPGAs (Field Programmable Gate Arrays),PLDs (Programmable Logic Devices), controllers, state machines, gatedlogic, discrete hardware components, or any other suitable circuitry, orany combination of circuits that can perform the various functionalitydescribed throughout this disclosure. Those skilled in the art willrecognize how best to implement the described functionality for theprocessing system depending on the particular application and theoverall design constraints imposed on the overall system.

The machine-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared (IR),radio, and microwave, then the coaxial cable, fiber optic cable, twistedpair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method for wireless communications, comprising:receiving and processing a first component carrier (CC) in a carrieraggregation scheme via a first receive path comprising a first low noiseamplifier (LNA) and a first mixer, wherein the first LNA is configuredto amplify the first CC and wherein the first mixer is configured tomultiply the amplified first CC with a first local oscillator (LO)signal received via a first LO path and generated by a first frequencysynthesizer whose output frequency is divided down by a first divideratio to create the first LO signal; adding or discontinuing receptionof a second CC in the carrier aggregation scheme, the second CC having adifferent frequency than the first CC; and based on the added ordiscontinued reception of the second CC, at least one of: retuning thefirst frequency synthesizer to a different output frequency; changingthe first divide ratio; or switching the amplified first CC from beingmultiplied by the first mixer to being multiplied by a second mixer withthe first LO signal received via a second LO path and generated by asecond frequency synthesizer whose output frequency is divided down by asecond divide ratio to create the first LO signal.
 2. The method ofclaim 1, wherein the first frequency synthesizer has the lowest currentconsumption of all frequency synthesizers for the carrier aggregationscheme when the first CC is the only component carrier.
 3. The method ofclaim 1, wherein the least one of the retuning, the changing, or theswitching is selected based on at least one of: current consumptionassociated with the first and second divide ratios and with the firstand second frequency synthesizers; or coupling between at least one ofthe first LO signal, the first component carrier, the second componentcarrier, a first or second harmonic of a transmit signal, or an LOsignal associated with the transmit signal.
 4. The method of claim 1,wherein adding reception of the second CC comprises receiving andprocessing the second CC via a second receive path comprising a secondLNA and a third mixer, wherein the second LNA is configured to amplifythe second CC, and wherein the third mixer is configured to multiply theamplified second CC with a second LO signal received via a third LO pathand generated by a third frequency synthesizer whose output frequency isdivided down by a third divide ratio to create the second LO signal. 5.The method of claim 4, wherein the third frequency synthesizer is thefirst frequency synthesizer.
 6. The method of claim 4, furthercomprising: adding or discontinuing reception of a third CC in thecarrier aggregation scheme, the third CC having a different frequencythan the first and second CCs; and based on the added or discontinuedreception of the third CC, at least one of: retuning at least one of thefirst, second, or third frequency synthesizer to a different outputfrequency; changing at least one of the first, second, or third divideratio; switching the amplified first CC from being multiplied by thefirst mixer to being multiplied by the second mixer; switching theamplified first CC from being multiplied by the second mixer to beingmultiplied by the first mixer; or switching the amplified first CC frombeing multiplied by the first or second mixer to being multiplied by afourth mixer with the first LO signal received via a fourth LO path andgenerated by a fourth frequency synthesizer whose output frequency isdivided down by a fourth divide ratio to create the first LO signal. 7.The method of claim 6, wherein adding reception of the third CCcomprises receiving and processing the third CC via a third receive pathcomprising a third LNA and a fifth mixer, wherein the third LNA isconfigured to amplify the third CC, and wherein the fifth mixer isconfigured to multiply the amplified third CC with a third LO signalreceived via a fifth LO path and generated by a fifth frequencysynthesizer whose output frequency is divided down by a fifth divideratio to create the third LO signal.
 8. The method of claim 7, whereinthe fifth frequency synthesizer is the first, second, third, or fourthfrequency synthesizer.
 9. The method of claim 7, further comprising:adding or discontinuing reception of a fourth CC in the carrieraggregation scheme, the fourth CC having a different frequency than thefirst, second, and third CCs; and based on the added or discontinuedreception of the fourth CC, at least one of: retuning at least one ofthe first, second, third, or fourth frequency synthesizer to a differentoutput frequency; changing at least one of the first, second, third, orfourth divide ratio; switching the amplified first CC from beingmultiplied by the first mixer to being multiplied by the second orfourth mixer; switching the amplified first CC from being multiplied bythe second mixer to being multiplied by the first or fourth mixer;switching the amplified first CC from being multiplied by the fourthmixer to being multiplied by the first or second mixer; or switching theamplified first CC from being multiplied by the first, second, or fourthmixer to being multiplied by a sixth mixer with the first LO signalreceived via a sixth LO path and generated by a sixth frequencysynthesizer whose output frequency is divided down by a sixth divideratio to create the first LO signal.
 10. The method of claim 9, whereinadding reception of the fourth CC comprises receiving and processing thefourth CC via a fourth receive path comprising a fourth LNA and aseventh mixer, wherein the fourth LNA is configured to amplify thefourth CC, and wherein the seventh mixer is configured to multiply theamplified fourth CC with a fourth LO signal received via a seventh LOpath and generated by a seventh frequency synthesizer whose outputfrequency is divided down by a seventh divide ratio to create the fourthLO signal.
 11. The method of claim 10, wherein the seventh frequencysynthesizer is the second frequency synthesizer and wherein the seventhmixer is the second mixer.
 12. The method of claim 9, wherein the sixthfrequency synthesizer is not the first, second, or third frequencysynthesizer.
 13. The method of claim 1, wherein the second CC is in adifferent Evolved UMTS (Universal Mobile Telecommunications System)Terrestrial Radio Access (E-UTRA) frequency band than the first CC. 14.An apparatus for wireless communications, comprising: a first frequencysynthesizer whose output frequency is divided down by a first divideratio to create a first local oscillator (LO) signal; a first receivepath configured to receive and process a first component carrier (CC) ina carrier aggregation scheme, the first receive path comprising: a firstlow noise amplifier (LNA) configured to amplify the first CC; and afirst mixer configured to multiply the amplified first CC with the firstLO signal received via a first LO path; and a processing systemconfigured to: add or discontinue reception of a second CC in thecarrier aggregation scheme, the second CC having a different frequencythan the first CC; and based on the added or discontinued reception ofthe second CC, at least one of: retune the first frequency synthesizerto a different output frequency; change the first divide ratio; orswitch the amplified first CC from being multiplied by the first mixerto being multiplied by a second mixer with the first LO signal receivedvia a second LO path and generated by a second frequency synthesizerwhose output frequency is divided down by a second divide ratio tocreate the first LO signal.
 15. The apparatus of claim 14, wherein thefirst frequency synthesizer has the lowest current consumption of allfrequency synthesizers for the carrier aggregation scheme when the firstCC is the only component carrier.
 16. The apparatus of claim 14, whereinthe processing system is configured to select the least one of theretuning, the changing, or the switching based on at least one of:current consumption associated with the first and second divide ratiosand with the first and second frequency synthesizers; or couplingbetween at least one of the first LO signal, the first componentcarrier, the second component carrier, a first or second harmonic of atransmit signal, or an LO signal associated with the transmit signal.17. The apparatus of claim 14, further comprising: a second receive pathcomprising a second LNA and a third mixer; and a third frequencysynthesizer, wherein the processing system is configured to addreception of the second CC by controlling receiving and processing ofthe second CC via the second receive path, wherein the second LNA isconfigured to amplify the second CC, and wherein the third mixer isconfigured to multiply the amplified second CC with a second LO signalreceived via a third LO path and generated by the third frequencysynthesizer whose output frequency is divided down by a third divideratio to create the second LO signal.
 18. The apparatus of claim 17,wherein the third frequency synthesizer is the first frequencysynthesizer.
 19. The apparatus of claim 17, wherein the processingsystem is configured to: add or discontinue reception of a third CC inthe carrier aggregation scheme, the third CC having a differentfrequency than the first and second CCs; and based on the added ordiscontinued reception of the third CC, at least one of: retune at leastone of the first, second, or third frequency synthesizer to a differentoutput frequency; change at least one of the first, second, or thirddivide ratio; switch the amplified first CC from being multiplied by thefirst mixer to being multiplied by the second mixer; switch theamplified first CC from being multiplied by the second mixer to beingmultiplied by the first mixer; or switch the amplified first CC frombeing multiplied by the first or second mixer to being multiplied by afourth mixer with the first LO signal received via a fourth LO path andgenerated by a fourth frequency synthesizer whose output frequency isdivided down by a fourth divide ratio to create the first LO signal. 20.The apparatus of claim 19, further comprising: a third receive pathcomprising a third LNA and a fifth mixer; and a fifth frequencysynthesizer, wherein the processing system is configured to addreception of the third CC by controlling receiving and processing of thethird CC via the third receive path, wherein the third LNA is configuredto amplify the third CC, and wherein the fifth mixer is configured tomultiply the amplified third CC with a third LO signal received via afifth LO path and generated by the fifth frequency synthesizer whoseoutput frequency is divided down by a fifth divide ratio to create thethird LO signal.
 21. The apparatus of claim 20, wherein the fifthfrequency synthesizer is the first, second, third, or fourth frequencysynthesizer.
 22. The apparatus of claim 20, wherein the processingsystem is configured to: add or discontinue reception of a fourth CC inthe carrier aggregation scheme, the fourth CC having a differentfrequency than the first, second, and third CCs; and based on the addedor discontinued reception of the fourth CC, at least one of: retune atleast one of the first, second, third, or fourth frequency synthesizerto a different output frequency; change at least one of the first,second, third, or fourth divide ratio; switch the amplified first CCfrom being multiplied by the first mixer to being multiplied by thesecond or fourth mixer; switch the amplified first CC from beingmultiplied by the second mixer to being multiplied by the first orfourth mixer; switch the amplified first CC from being multiplied by thefourth mixer to being multiplied by the first or second mixer; or switchthe amplified first CC from being multiplied by the first, second, orfourth mixer to being multiplied by a sixth mixer with the first LOsignal received via a sixth LO path and generated by a sixth frequencysynthesizer whose output frequency is divided down by a sixth divideratio to create the first LO signal.
 23. The apparatus of claim 22,further comprising: a fourth receive path comprising a fourth LNA and aseventh mixer; and a seventh frequency synthesizer, wherein theprocessing system is configured to add reception of the fourth CC bycontrolling receiving and processing of the fourth CC via the fourthreceive path, wherein the fourth LNA is configured to amplify the fourthCC, and wherein the seventh mixer is configured to multiply theamplified fourth CC with a fourth LO signal received via a seventh LOpath and generated by the seventh frequency synthesizer whose outputfrequency is divided down by a seventh divide ratio to create the fourthLO signal.
 24. The apparatus of claim 23, wherein the seventh frequencysynthesizer is the second frequency synthesizer and wherein the seventhmixer is the second mixer.
 25. The apparatus of claim 22, wherein thesixth frequency synthesizer is not the first, second, or third frequencysynthesizer.
 26. The apparatus of claim 14, wherein the second CC is ina different Evolved UMTS (Universal Mobile Telecommunications System)Terrestrial Radio Access (E-UTRA) frequency band than the first CC. 27.A non-transitory computer-readable medium for wireless communications,the medium having instructions stored thereon, which are executable to:receive and process a first component carrier (CC) in a carrieraggregation scheme via a first receive path comprising a first low noiseamplifier (LNA) and a first mixer, wherein the first LNA is configuredto amplify the first CC and wherein the first mixer is configured tomultiply the amplified first CC with a first local oscillator (LO)signal received via a first LO path and generated by a first frequencysynthesizer whose output frequency is divided down by a first divideratio to create the first LO signal; add or discontinue reception of asecond CC in the carrier aggregation scheme, the second CC having adifferent frequency than the first CC; and based on the added ordiscontinued reception of the second CC, at least one of: retune thefirst frequency synthesizer to a different output frequency; change thefirst divide ratio; or switch the amplified first CC from beingmultiplied by the first mixer to being multiplied by a second mixer withthe first LO signal received via a second LO path and generated by asecond frequency synthesizer whose output frequency is divided down by asecond divide ratio to create the first LO signal.
 28. An apparatus forwireless communications, comprising: means for synthesizing a firstfrequency; means for frequency dividing the first frequency by a firstdivide ratio to create a first local oscillator (LO) signal; means forreceiving and processing a first component carrier (CC) in a carrieraggregation scheme, comprising: means for amplifying the first CC; andfirst means for mixing the amplified first CC with the first LO signalreceived via a first LO path; means for adding or discontinuingreception of a second CC in the carrier aggregation scheme, the secondCC having a different frequency than the first CC; and means forselecting, based on the added or discontinued reception of the secondCC, between at least one of: retuning the means for synthesizing thefirst frequency to a different output frequency; changing the firstdivide ratio; or switching the amplified first CC from being mixed bythe first means for mixing to being mixed by a second means for mixingwith the first LO signal received via a second LO path and generated bymeans for synthesizing a second frequency that is divided down by asecond divide ratio to create the first LO signal.